The present invention relates generally to methods for the fabrication of high temperature strength engine components, and more particularly to a co-extrusion method for manufacturing gas turbine engine disks for high temperature operation.
In the operation of gas turbine engines, temperatures encountered by engine components require that a rotating turbine disk within the engine preferably exhibit high temperature resistance to creep and stress rupture in the rim of the disk, and high temperature ultimate tensile strength in the bore. Typical rotating engine components which are exposed to high operating temperatures and wherein strength characteristics in the rim different from that of the bore are desirable include components in all stages of the compressor spool and all other turbine disks exposed to hot gas flow downstream of the combustor region of the engine. Prior art fabrication methods for engine disks having different rim/bore materials consist chiefly of inertia welding a bore or web of preselected material, size and configuration to a ring of different material and corresponding size comprising the rim of the finished disk. In the inertia welding process, the bore/web is rotated at preselected high speed and pushed against the stationary rim to generate by friction heat required to make a weld between bore and rim. The heat affected zone in such welds is characteristically narrow as compared to that obtained by fusion welding processes. Engine disks fabricated by the inertia welding process chiefly consist of bores of titanium base and nickel base superalloy fatigue (low and high) and/or burst (high ultimate tensile strength) resistant type metals and alloys, including Ti6-4, Ti-17, Ti6-2-4-6, Rene-95, Inco-718, Merl-76, In-100, and Rene-88DT, and rims of respective similar metals and alloys, including Ti6-2-4-2, IMI-829, Astroloy, R-88DT, In-100, U-500, U-700, U-720, and Rene-41, wherein a respective pair of materials must be selected for amenability to welding by the inertia process. The inertia welding process for fabricating engine disks therefore suffers from certain shortcomings including limitation on bore/rim material selection to those combinations amenable to inertia welding. undesirably low attainable heat affected zone/weld thickness between bore and rim. low strength or embrittlement of the material in the bore/rim weld interface, and machine oapacity limitations due to large weld surface areas and/or large diameters.
The invention solves or reduces in critical importance problems with prior methods associated with the fabrcation of engine disks for turbine engines by providing a co-extrusion method for fabricating gas turbine engine disks having high temperature resistance to creep and stress rupture in the rim and high tensile strength and/or high fatigue (low) or crack growth rate resistance in the bore or web, wherein the two materials comprising. respectively, the rim and bore of the disk are simultaneously co-extruded at a appropriate preselected extrusion temperature from a preform billet of the two materials, resulting in a solid state metallurgical bond between the two materials, the extrusion being subsequently processed thermomechanically (e.g. by forging) and/or machined to achieve the desired shape or to perform appropriate mechanical work reductions to desired product size. The method of the invention allows formation of disks from substantially any combination of materials desired for the rim and bore, respectively. and, accordingly, preferred combinations of titanium base and nickel base superalloy fatigue (low and high) and/or burst (high ultimate tensile strength) resistant type metals and alloys, including Ti6-4, Ti-17, Ti6-2-4-6, Rene-95, Rene-88DT, In-400, and Merl-76, for the bore and creep rupture resistance type metals and alloys, including Ti6-2-4-2, IMI-829, Udimet-500, Udimet-700, Udimet-720, and Astroloy, for the rim may be used, many of which which were not practical using prior disk fabrication methods (e.g., inertia welding). The preform billet may comprise any combination of wrought, powder or cast material in any combination of alloys in any number of concentric layers (rings) to achieve desired product characteristics. Components fabricated from extrusions made according to the invention have improved and predictable metallurgical and structural properties as compared to those made by the more expensive inertia welding process.
It is therefore a principal object of the invention to provide an improved method for fabricating high temperature resistant gas turbine engine disks.
It is a further object of the invention to provide a method for fabricating gas turbine disks by co-extrusion.
It is a further object of the invention to provide an improved gas turbine engine disk fabricated by co-extrusion.
These and other objects of the invention will become apparent a the detailed description of representative embodiments proceeds.